The present invention relates to a telescopic extraction arm intended for use as localized extraction for welding fumes, powder, dust etc., specified in the preamble to. The arm may be used separately or may form part of systems, in which the extracted air passes through a filter arrangement before reaching an associated fan unit.
Previously known telescopic arrangements comprise two tubes, an outer tube and an inner tube moveable in relation to one another. The inner tube, arranged so that it can move inside the outer tube, is supported by a slide bearing sleeve situated at the outer end of the outer tube. The slide bearing sleeve is slotted over its entire length and can be partly fixed in the outer tube and partly secured against the inner tube by means of adjusting screws arranged in the outer tube. Owing to the longitudinal slotting, the sleeve is opened to a larger diameter in the event of torsional loading of the outer end of the inner tube and if the adjusting screws are at the same time screwed out. Due to the play in the opened slide bearing sleeve, the inner tube will be slanted in relation thereto, which means that the inner tube only bears against the edges of the slide bearing sleeve and a xe2x80x9cdrawer effectxe2x80x9d occurs, making adjustment more difficult. Should the adjusting screws be screwed in on the other hand, the slide bearing sleeve will indeed be closed up and the diameter reduced, but the friction against the inner tube will at the same time increase, which likewise makes adjustment more difficult.
The object of the invention is to provide an extraction arm, which makes handling and adjustment of a suction device to selectable working positions within the space available easier than hitherto. This is feasible with an extraction arm of the generic type that has the characteristic features specified in the claims below. Preferred embodiments and advantageous developments and refinements to the invention will be evident from the description and the dependent claims.